1. Field of the Invention
This invention relates to a complex skin of the type used for exposed decorative surfaces and, more particularly, to a skin made by slush molding a thermoplastic elastomer composition. The invention is also directed to an article which incorporates the complex skin.
2. Background Art
It is known to perform a powder slush molding process using a soft vinyl chloride resin powder to produce a wide range of skins, as for articles in automobile interiors, such as instrument panels, console boxes, door trims, etc. This process allows a skin to be formed which is soft to the touch and which can be crimped and stitched. The process further allows a high degree of design freedom.
Unlike other molding processes, such as injection molding and compression molding, the powder slush molding process does not produce a particular shape under pressure. The powder fluidity may not be sufficient to cause uniform adherence to a mold with a complex shape. Preferably, the powder material should have a sufficiently low melt viscosity to form a film when the powder adhering to a mold is melted without the application of pressure.
It is also desirable that the molded skin be readily releasable from a mold by cooling the mold.
In JP-A7-82433, it is proposed to use a ground mixture of polypropylene resin and a specific styrene-series thermoplastic elastomer at a weight ratio of 70/30 to 30/70. The styrene-series thermoplastic elastomer is selected from a styrene/ethylene-butylene/styrene block copolymer with a styrene content equal to or less than 20% by weight, a styrene/ethylene-propylene/styrene block copolymer with a styrene content equal to or less than 20% by weight, and a hydrogenated styrene-butadiene random copolymer rubber with a styrene content equal to or less than 20% by weight. The styrene-series thermoplastic elastomer is readily miscible with the polypropylene resin. The resulting composition is described to be suitable for powder molding.
The composition is suitable for forming a skin material because hydrogenated styrene-butadiene random copolymer rubber can be finely dispersed in the polypropylene resin when the polypropylene resin is mixed with the hydrogenated styrene-butadiene random copolymer rubber. Less deterioration of the physico-chemical properties results. However, when this composition is used as the inner layer of a complex skin having an outer and inner layer, oligomer components, a process oil, a stabilizer, and a catalyst in the composition tend to bleed to the surface of the skin to make the resulting skin viscous. This is because the hydrogenated styrene-butadiene random co-polymer rubber has poor oil absorption capability.
If a transparent coating film is formed and thermally applied on the surface of the outer layer of the complex skin so as to effect reinforcement thereof, the process oil, stabilizer, and catalyst in the inner layer, in addition to the oligomer components therein, bleed to the surface over time, eventually deteriorating the adhesion of the complex skin to an underlying urethane foam. Because the powder of the thermoplastic elastomer composition defining the inner layer is below ambient temperature during the slush molding process, the oligomer components, the process oil, the stabilizer, and the catalyst in the composition bleed to the surface of the powder, which turns the powder to a viscous state. The composition may cause blocking over time as a result of which the powder fluidity deteriorates. Releasability of the skin from a mold may likewise be deteriorated. The skin may be deformed upon being released from the mold.
Generally, the skins prepared using conventional thermoplastic elastomer compositions have not both satisfactorily adhered to a mold and permitted release from the mold. Conventionally, thermoplastic elastomer compositions have been modified to improve releasability, while primers or adhesives have been coated on a mold so as to enhance the adhesion. However, the skin, after such adhesive treatment, tends to remain viscous at the treated area thereof, so that the resulting skin cannot be stacked, as for storage. Thus, a considerable amount of space may be required to store such skins.
The invention is directed to a multilayer skin having an outer layer and an inner layer. The outer layer is prepared by slush molding powder of a thermoplastic elastomer composition having a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, and a release agent. The inner layer is bonded to the outer layer, is prepared by slush molding, and is a blend of an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, and a catalyst which promotes isocyanate reaction.
The invention is also directed to a multilayer skin having an inner layer and an outer layer. The outer layer is prepared by slush molding the powder of a thermoplastic elastomer composition including at least a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, and a release agent. The inner layer is prepared by slush molding first and second powders. The first powder is made from a thermoplastic elastomer composition including a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, and an elastomer with high oil absorption capability. The second powder includes an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, and a catalyst promoting isocyanate reaction.
The invention is also directed to an article including a core layer made of synthetic resin, a multilayer skin having an inner layer and an outer layer bounded to the inner layer, and a foam layer between the core layer and the multilayer skin. The foam layer is bonded to the multilayer skin and to the core layer. The outer layer of the multilayer skin is prepared by slush molding the powder of a thermoplastic elastomer composition that is made from a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, and a release agent. The inner layer of the multilayer skin is made from an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, and a catalyst which promotes isocyanate reaction.
The invention is also directed to an article having a core layer made from a synthetic resin, a multilayer skin having an inner layer and an outer layer bonded to the inner layer, and a foam layer between the core layer and the multilayer skin. The foam layer is bonded to the multilayer skin and the core layer. The outer layer of the multilayer skin is prepared by slush molding powder of a thermoplastic elastomer composition made from a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, and a release agent. The inner layer is prepared by slush molding first and second powders. The first powder is a thermoplastic elastomer composition including a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, and an elastomer with high oil absorption capability. The second powder is an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, and a catalyst promoting isocyanate reaction.
The invention is also directed to a multilayer skin having inner and outer layers each prepared by slush molding powder. The powder in the outer layer is a thermoplastic composition including a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, and a release agent. The inner layer includes a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, and a catalyst providing isocyanate reaction.
The invention is further directed to a multilayer skin having inner and outer layers each prepared by slush molding powder. The powder in the outer layer is a thermoplastic composition including a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, and a release agent. The inner layer is prepared by slush molding first and second powders. The first powder is a thermoplastic elastomer composition including a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, and an elastomer with high oil absorption capability. The second powder is a thermoplastic composition including a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, and a catalyst promoting isocyanate reaction.
The invention is also directed to an article having a core layer made from a synthetic resin, a multilayer skin having an inner layer and an outer layer each prepared by slush molding powder, and a foam layer between the core layer and the multilayer skin. The foam layer is bonded to the multilayer skin and to the core layer. The outer layer is prepared by slush molding powder made from a thermoplastic elastomer composition including a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, and a release agent. The inner layer is prepared by slush molding powder made from a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, and a catalyst promoting isocyanate reaction.
The inner layer may further include a release agent.
The foam layer may be polyurethane foam.
The core layer may be an olefinic resin.
In one form, the outer layer has a surface and a coating film is formed on the surface of the outer layer.
The elastomer with high oil absorption capability in one, or both, of the inner and outer layers may be an ethylene-octene copolymer.
The ratio of the first powder to the second powder may be 1:5 to 5:1.
The invention is further directed to a thermoplastic elastomer composition for use in forming, by slush molding, an inner layer of a multilayer skin having an inner layer and an outer layer. The thermoplastic elastomer composition is made from a polypropylene resin, a hydrogenated styrene-butadiene random copolymer rubber, a process oil, an elastomer with high oil absorption capability, an olefinic polymer with active hydrogen, a catalyst promoting isocyanate reaction, and a release agent.
The elastomer with high oil absorption capability may be an ethylene-octene copolymer with a long-chain branched structure.